Filling blue carbon knowledge gaps

New Charles Darwin University (CDU) research highlighting the need to preserve the world’s mangrove forests has been published in the scientific journal “Global Change Biology”.

Mangrove forests hold substantial amounts of organic carbon, or blue carbon, for their area – sometimes three to five times larger per unit area compared with forest environments in the same region.

PhD candidate at CDU’s Research Institute for the Environment and Livelihoods, Sigit Sasmito said not only were the 13.7 million hectares of mangroves globally reducing at a rapid rate, but disturbing carbon-dense mangroves also resulted in very high greenhouse gas emissions.

“While mangroves are great at storing carbon, it’s not removed from the environment. So disturbing mangroves, through land use changes such as aquaculture, causes this stored carbon to be released. On top of that, disturbance means the ongoing carbon storage benefits are also lost or reduced,” he said.

“But little research has been done to assess the impact of these factors on carbon management and there is no global consensus on blue carbon change when mangroves are deforested. Our research reviewed existing knowledge to help shed light on this.”

Over the past decade, it has been estimated that the reduction in mangroves has caused the release of the equivalent of 6% of the world’s annual carbon emissions from land-use sector.

Mangroves are the subject of a wide range of degradation and deforestation impacts. In South-east Asia, the largest threat to mangroves is clearing for the construction of aquaculture ponds.

Sigit said that while mangroves were quick to disappear they were slow to regenerate.

“It can take about 40 years for mangroves to regenerate in terms of their carbon storage capability. It can be even longer in some cases depending on physical factors such as location and climate and whether the mangroves were actively being rehabilitated or restored,” she said.

To better understand the greenhouse gas emission impact of mangrove disturbance, Sigit’s research has produced a global-scale dataset that helps address the significant knowledge gaps relating to blue carbon dynamics.

“The data assembled through this research can help climate change policy makers better identify greenhouse gas emissions associated with the loss of mangroves and the carbon removal created through mangrove reforestation programs.

“This allows blue carbon ecosystems such as mangroves to be included in national-scale climate change mitigation policies,” Sigit said.

The research also paints a case for better management and conservation of mangroves.

“We know they do a great job at storing carbon and our research has better identified the carbon emission implications of removing mangroves.

“But ultimately, what the research really shows is we need improved management of mangroves focusing on conservation and restoration to prevent further loss and the associated carbon emissions,” Sigit said.